Hey all!

Just got done with a three-day work session with a couple buddies and I wanted to type up some notes and feedback from what we did so that maybe someone can find this information helpful in the future. I'll keep each section to one specific item-related topic. For reference, I have a base model 1990 auto coupe with 73k miles with no modifications prior to these I will list below.

Cat-less front y-pipe and high-flow catalytic converter from Exotic Muscle
Merle, the owner of EM, was great to order from. For the most part, these parts went on pretty easily. There were some minor fitment issues just because the front y-pipes are pre-fab. We had to use a jack to push up on the joint between the back y-pipe and the cat to get the exhaust to fit into the bracket/clamp after the bolts connecting the exhaust manifolds to the front y-pipe were tightened since the cat was sagging a bit, but that was really it. We did need to cut about 0.5" to 1" off of the A.I.R. tube on the cat so that the cat was far enough forward on the car to clamp onto the front y pipe. Without cutting some of the tube off, there would have only been an overlap of about 1/8" an I didn't feel comfortable with that. Furthermore, with the A.I.R. pipe that leads to the cat, it is flanged, which makes connecting that to the tube on the cat easy, but it stops the cat eventually from moving any further forward. The other issue with this fitment was that a clamp was not provided to connect the A.I.R. tube to the cat, so I had to buy a standard hose clamp and tightened that down. Below is a YouTube video with the stock L98 exhaust system (no engine modifications) followed by a video of my new exhaust. To clarify, my exhaust is now an Exotic Muscle cat-less front y-pipe, Exotic Muscle hi-flow catalytic converter, stock rear y-pipe that has a couple holes, and stock mufflers. Once I get some more video with the new exhaust components installed, I'll put together a compilation video of before and after and post it below, if I can remember lol.

KYB shocks and Energy Suspension poly bushings
Overall, this job was easy. I liked the idea of using polyurethane bushings for both the front and rear upper shock mounts, so I ordered black Energy Suspension bushings from Zip Corvette (which, by the way, are generic upper shock mount bushings, they are not C4 specific). When working on the front shocks, my initial understanding was to torque the top shock nut to what the FSM says, which I think was 19 ft-lbs but don't quote me. We hadn't even gotten to 10 ft-lbs and the poly bushing was pancaking. We backed off because it didn't feel right. After some research, I have come to the conclusion that the torque spec for that night was decided by GM for the specific bushings they made of a specific material in a specific shape and 19 ft-lbs was the right torque. With different bushings made of different materials (rubber included) in a different shape, we can't use the FSM torque spec for this nut. I called Energy Suspension to see what they think it should be torqued to and after a 10 min conversation, they decided it'd be best to tighten the nut until the bushings bulge slightly outside the washer KYB provided while the weight of the car is on the wheels. Maybe everyone knows this already, but I saw so much conflicting info online that I wanted to share exactly what Energy said. Another thing I wanted to mention was that the rear shock's upper mount poly bushings did not fit completely with the KYBs. (I don't know if this is true on all shocks for our cars.) By the time you place the bottom washer, the bottom bushing, the bracket, the top bushing, and the top washer, there are no threads for the nut to grab onto to tighten everything down accordingly. I ended up using a poly bushing for just the bottom bushing and using one of the rubber bushings KYB provided for the top bushing because I wanted more stiffness out of the shock's bushing setup and I figured I'd get more of what I wanted if the poly bushing were on the bottom than if it were the one on top. Finally, marine grease, which I used very liberally seems to be working great with the poly bushings. In the limited amount I've driven the car so far, I've heard no squeaks. And while I can't speak on the quality of the KYBs specifically, what a difference these shocks are compared to the old ones; they felt fantastic on the road. My buddy could compress the original Delco shocks with one hand on each end, but he couldn't budge the KYBs.

Vette2Vette No-Flex kit
Installing this kit only had one problem. The front bracket is definitely a breeze to put on, as is putting the bars between each side's brackets. But the rear brackets, are what I want to provide a lot of info for. The first issue we ran into was after lightly installing the rear bracket was using the transfer punch to mark where to drill the hole in the frame. There is so little room to swing your hammer to punch a reasonable indentation in the frame. We did as much as we could before pulling the bracket off and attempting to drill the hole and the drill bit still drifted. So we decided to put the bracket back on and drill the hole with the bracket in place and it was much easier. Did we shave off a tiny bit of the hole in the bracket? Yeah, a tiny bit, but it really did not become oblong or enlarge. Make sure when drilling the hole that you use pressure and not speed to drill your hole, and use metal drilling oil (CRC makes a can for like $5). Eventually, with patience you punch through. I will also add that in the Motortrend article with the detailed steps and pictures, when you zoom in on the picture they have after their hole is drilled, we thought it looked like they drilled their hole with the bracket on too. Once the hole was drilled, we went to install the bolt that goes through it and the bolt on the right side ended up stripping. We bought a nut splitter which is such an awesome tool if you don't have one, it worked perfectly. Highly recommend, especially for $15. Once it was off, I called Jason at Vette2Vette to get the hardware specs to buy a new bolt and nut and he said it was a 3/8" size 16 flange head bolt, 1" long, in grade 5. My buddy and I decided to improve on their hardware and got a grade 10 bolt with thinner threads than what Vette2Vette provided and, honestly, we would recommend anyone installing this system to just go out and get grade 8 or 10 hardware to replace all of the hardware Vette2Vette provided just because we thought grade 8 or 10 is more practical and stronger. Not required just recommended. HERE'S THE BIGGEST THING THOUGH: Jason actually said that drilling the bottom hole is NOT required and many ZR1 owners that install the kit don't drill the hole and it works fine. As long as you torque down the top bolt on the rear brackets to spec, the bracket won't go anywhere, especially once the bars are tightened down. We really wish this was information was provided in the instructions because we likely would not have taken the time or effort to drill the holes. In terms of the results of installing the system, it did make a measurable difference. We we measured the distance from the windshield to the halo with the weight of the car on its wheels, we got 21.5". When the suspension was suspended on jack stands, the distance was 21.75". We went back and forth between tightening with weight on wheels and lifting onto jack stands until both measurements were the same at 21 15/16". I haven't had a chance to drive the car yet since installing this kit, but I do feel more at ease knowing that it physically made a difference. We'll see how it feels. Maybe it won't change much, but I can see it being a preventative addition to the car too. Last thing I'll add is that the bars do take away the ability to jack up the entirety of one side of the car from the frame rail, so I'll need jack the front from the cross brace and eventually manufacture an I-beam to jack the rear up from the differential without hitting the exhaust pipes.

Wheel speed sensor wire wrapping
My wheel speed sensor wires were disintegrating, cracking, and covered in a white mold-looking substance. I took them off carefully, picked off the remaining rubber-like material covering the wires themselves, and wrapped them in Scotch Super 33+ first followed by 1/4" split loom. It was easy and hopefully will protect these things for a long time, because to my understanding they're unobtanium, you can't find them anywhere if they get damaged.


Wheel speed sensor wrapped in Super 33+ and split loom


Hatch release cable with crimp lug
Just a little addition I made that I also wanted to recommend to everyone. I attached a 12-10 gauge 1/4" ring terminal to the rear hatch release cable that sits under the trunk cover with a crimper and hooked on a keychain ring. What a relief it is to not have to carry around channellocks while my hatch release buttons don't work. I also imagine this is a great addition for everyone even if your switches work just incase something does go wrong in the future and you don't have pliers, that wire is impossible to grip and pull with your fingers.